Socially-facilitated excessive drinking is common in adolescence, and social relationships remain a primary factor in alcohol intake throughout life. Patterns of social binge drinking can have many direct negative consequences, and have the potential to lead to later alcohol abuse. By understanding the biological and social influences on excessive drinking we can begin to prevent and treat alcohol use disorders. The objective of the proposed studies is to understand the effects of social affiliations on alcohol drinking in a novel animal model for this behavior, the prairie vole, which exhibits strong social bonds and a naturally high intake of alcohol. This objective will be addressed with the following three aims: 1 Elucidate dyadic interactions in patterns of alcohol intake, and their effects on drinking levels. To test the social influence on alcohol intake patterns, 'high drinkers' will be paired with 'low drinkers,' designated as such during a two-bottle choice test with water and 10% alcohol in social isolation. The alcohol intake of each animal will be monitored using a lickometer system, to determine whether the drinking level of one or both animals changes in the paired condition. Subsequently, alcohol intake in a second isolation will be assessed to determine whether changes in drinking during social housing persist even without continuing social influence. Further, the pattern of drinking of each vole will be assessed to determine whether there are social interactions influencing timing of drinking such as one animal drinking before the other, or simultaneous drinking. 2 Determine whether social dominance is linked with influential drinking behavior. As in 1, high and low drinkers will be paired to assess drinking. Before pairing, the voles will be introduced in the social dominance tube task to determine which vole exhibits more dominant behavior, evidenced by pushing the other animal back to its starting cage through a narrow tube. Association between dominance and initial drinking level, propensity to adjust alcohol preference, and propensity to initiate drinking bouts will be assessed. 3 Determine whether vasopressin V1a receptor microsatellite length or binding level affects social drinking or dominance behavior. DNA samples acquired from tails from the animals used in 1 and 2 will be used to determine microsatellite length by amplification of the region within the V1aR promoter using polymerase chain reaction, followed by fragment length analysis. Brains from the same animals will be used to determine V1aR binding level by autoradiography, using a 125I- linear-AVP antagonist as a ligand for the V1aR. Then correlations between microsatellite length or receptor binding density in discrete brain regions and initial drinking level, change in alcohol intake, and dominance behavior will be analyzed to determine whether this genetic factor or receptor levels correspond with social and drinking behaviors. Discovery of social factors that can directly affect alcohol drinking behavior, or genetic factors that can influence social and/or alcohol drinking behavior is important in furthering understanding of the emergence or progression of alcoholism, and in developing new prevention or treatment strategies. PUBLIC HEALTH RELEVANCE: Alcohol use disorders are a prevalent problem that can lead to health, financial, social, and legal problems that affect not only individuals but society as a whole. The proposed work seeks to understand and ultimately prevent or treat the progression from social drinking to alcohol abuse, by uncovering biological and environmental factors that influence alcohol intake in an animal model of socially-facilitated excessive alcohol drinking.